Is there a review site out there that gives and estimation to how long a game with last/how many hours it will take to beat? I know there is a ton of room for error in this regard (especially with free roaming games like GTA and all) but I like to have some kind of idea as to what I'm getting into.

The only games who's hours seem to get reported in reviews is if the play time is either short (Beyond Good and Evil) or really long( KOTOR).

I see a lot of reviewers give time estimates for games, but take it with a grain of salt. When a reviewer plays a game, they try and get through it as quickly as possible. This may or may not be the way everybody else approaches a particular game.

Kotor is actually pretty short if you play Dark Side and don't do any side quests.

I know it is a YMMV situation as well, but I too find it useful info before starting a game. If I know I won't have a lot of time to play in the coming weeks, I want something a little shorter. Instead of starting the long game and very likely forgetting what I was doing, and having to replay early levels or whatnot.